In railroad locomotive operations, the throttle, dynamic brake and reverser actions of the locomotive, locomotives or other drive units, are controlled by the operator or engineer in the cab of the lead unit by manipulating three handles extending from the control stand, one handle each for throttle, dynamic brake, and reverser. The throttle handle, of course, controls the development of the tractive effort of the locomotive; i,e, the diesel engines or other power units. The dynamic brake handle controls the development of a retarding force known a dynamic brake, for example the electric motors driving the locomotive wheels, to place them in either motor mode where they will drive the wheels, or in generator mode, where they will function as a retarding force. The reverser handle controls the forward and reverse rotation of the electric motors to selectively drive the train forward or rearward, and includes a neutral position. Pursuant to current practice, the control stand is designed to be a man-to-machine interface and ideally is strictly an electronic/electric device having no direct mechanical, hydraulic or pneumatic connections the devices controlled. Instead, encoding means are preferably provided within the control stand to read and interpret the positions of the three handles, and convey appropriate signals, indicative of such positions, to an associated microcomputer. The associated microcomputer is programmed to interpret the encoded signals regarding the positions of the throttle, dynamic brake and reverser handles, as positioned at the control stand, and then electronically issue corresponding commands to manipulate the devices intended within the locomotive or locomotives. When utilizing a microcomputer, the throttle, dynamic brake and reverser commands effected at the control stand, are dependent upon the given angular positions of the three control handles, which are normally sensed and monitored by rotary encoding devices, which are mechanically coupled to associated rotary axles to which the control handles are secured, utilizing cams to actuate microswitches or contacts to provide a signal to the microcomputer as noted above. Such mechanical devices leave a lot to be desired, in that they do not provide the exacting degree of handle position determination as desired, are prone to mechanical failure, are cumbersome, space consuming, and require frequent adjustment.
With regard to the throttle and dynamic brake controls in particular, there is a need for more accurate and absolute encoder determinations because these controls can be set over a rather wide range of setting. The reverser control, on the other hand, is positionable to only three positions, namely, a "neutral" position at the center, and "forward" and "reverse" positions at either end. Accordingly, with regard to the reverser control, there is no need for any costly and complicated encoder technique to determine an absolute and exacting control handle position or command, as all that is necessary to determine is in which of the three positions the handle is located, namely, "forward", "reverse" or "neutral". Nevertheless, the prior art mechanically linked encoding mechanisms leave much to be desired, particularly with regard to determining and encoding the positions of the throttle and dynamic brake control handles.
There has been considerable development effort in the recent past to improve the encoder technology, particularly with regard to obtaining a more absolute determination and reading of the control handle positions. U.S. Pat. No. 5,036,468, issued on Jul. 30, 1991 to the same assignee as this invention, for example, discloses a new encoder apparatus and technique which is electronic rather than mechanical, to encode the absolute position of a pair a brake handles, on a train brake controller, one handle for operating the locomotive brakes and the other for operating the brakes on cars of the train. In that patented process, encoder means, such as optical encoders, are employed to optically determine the positions of the two brake handles, and produce a binary signal representative of those positions. With regard to each brake handle, the binary signal is converted to an analog signal, and electronically compared to a stored signal representative of the initial brake release position, to ascertain the difference between the newly selected position and the initial brake release position. An enabling means permits passage of the difference between the two positions when the newly selected brake position is greater than the initial brake release position, with the enabling means converting the analog signal back to a binary signal which is conveyed to the brake control apparatus to signify the actual brake change necessary. While this patented system is a significant improvement over prior art mechanical encoding techniques, it is specifically designed for a train brake control stand, and not particularly adaptable to a throttle control stand, as its circuitry, with signal converters and summing circuits, is more complicated than desired for a throttle control stand.
While more simplified use of optical encoders have been suggested, specifically attaching a rotary optical encoder directly to the end of the rotatable axle, such a concept would not make full utilization of the encoder's capabilities. This is because most optical encoders have sensing capabilities throughout a full rotational movement thereof; i.e., through a full 360 degrees. On the other hand, the limited pivotal nature of the control handles on the control stand, permits only a partial rotation of the handle, or axle to which it is attached. Since such pivotal rotation is normally limited to pivotal angles of less than 90 degrees, the optical encoder would necessarily be limited to the same rotational movement; i.e., less than 90 degrees. Accordingly, less than one fourth of a encoder's rotational capacity would be utilized, so that the encoder's degree of sensitivity would also be reduced to a value of less than one fourth of its capability.